Summary:

You could fly throigh a ceiling with elytra.

How to reproduce:

1.Make sure you are in survival mode.

2.Fly towards a ceiling with elytra and firework rockets(it is easier to reproduce if the filght of rockets are 3).

3.When you reach the ceiling, press "space" twice.

4.Then you will fly through the ceiling.

Analysis:

When you press space the first time, you will exit gliding, and your hitbox will update from 0.6 blocks to 1.8 blocks, so you will stuck in the block upon you. When you press space the second time, you will start to glide again. At this time, the thrust of rocket doesn't end, so you could go through the block you stucked in.

There is a video attached.